Looking at all the suggestions here I think that we should shift the paradigm (and I hate to use that word).
The item in question is decorative only (not a working motor). So, someone (Dave) will design a nice scale model of it which will resemble a real one. But if it is designed to fit one of the existing model trucks, it will be totally out of proportion. Why? Because the operational N scale trucks have way oversize sideframe thickness and even the wheels and axles are not truly scaled to 1:160 size.
Why not 3D-design and print the entire truck, which which would include it all: the sideframes, the wheels and the motors themselves? While I know that it will not be made 100% true to scale (due to material thickness limitation even in FXD), it would be much closer in appearance to the real one than an undersized traction motor installed in way-oversize N scale truck from a working model.
Since it will be a detail item prominently displayed, it would be nice it the detailed truck with motors looked more to scale. Plus if the traction motor is available as a separate part, it will look more in-scale if its dimensions aren't based on the existing N scale (operational) trucks and whelsets.